A multi-shaft fluid energy machine, for example, a multi-shaft gas turbine engine, has a plurality of compressor components, at least one combustion chamber and a plurality of turbine components. Thus, a dual-shaft gas turbine engine has a low-pressure compressor, a high-pressure compressor, at least one combustion chamber, a high-pressure turbine, as well as a low-pressure turbine. A triple-shaft gas turbine engine has a low-pressure compressor, a medium-pressure compressor, a high-pressure compressor, at least one combustion chamber, a high-pressure turbine, a medium-pressure turbine, and a low-pressure turbine.
FIG. 1 shows a highly schematized detail of a multi-shaft gas turbine engine in the area of a rotor 10 of a high-pressure turbine 11, as well as of a rotor 12 of a low-pressure turbine 13. Extending between high-pressure turbine 11 and low-pressure turbine 13 is an intermediate housing 14 having a crossflow channel 33 for delivering the flow exiting high-pressure turbine 11 to low-pressure turbine 13, at least one supporting rib 15 being positioned in crossflow channel 33.
Supporting rib 15 is a stator-side component that directs the flow traversing crossflow channel 33. Such a flow-directing supporting rib 15 has a leading edge 16, also referred to as a flow entry edge, a trailing edge 17, also referred to as a flow exit edge, and side walls 18.
A cavity 19 can open through from a radial outer region (see FIG. 1) into crossflow channel 33 upstream of supporting ribs 15 in the area of an entry into crossflow channel 33, respectively in the area of a leading edge 34 of intermediate housing 14, and cooling air 21a can be discharged through the same to a small degree and mix with gas flow 20 exiting high-pressure turbine 11. This cavity 19 is located between the HPT housing and intermediate housing 14 and is sealed by a seal 21c. Only a weak leakage flow 21b flows through this seal 21c since the HPT housing and intermediate housing 14 cannot be permanently joined to one another.
To allow leakage 21a to enter into crossflow channel 33 and prevent gas flow 20 from flowing in via cavity 19, the static pressure of gas flow 20 in the inlet zone of cavity 19 is below the pressure of cooling air 21b in secondary air zone 21d outside of the annular space.
As can be inferred from FIG. 2, in the case of the related-art fluid energy machine in accordance with FIG. 1, a pressure rise +Δp in the static pressure ensues upstream of leading edges 16 of supporting ribs 15 due to a blocking of the gas flow traversing crossflow channel 33 at circumferential positions where the supporting ribs are positioned, whereas in accordance with FIG. 2, a pressure drop −Δp in the static pressure ensues at circumferential positions between adjacent supporting ribs 15. A dimensionless circumferential direction u/t is shown in FIG. 2, t corresponding to the supporting rib pitch in circumferential direction u.
The pressure fields of pressure rise +Δp illustrated by dashed lines in FIG. 2 at the circumferential positions of supporting ribs 15 and of pressure drop −Δp at the circumferential positions between adjacent supporting ribs 15, upstream of leadings edges 16 of supporting ribs 15, respectively, extend into cavity 19, so that a dissipative secondary flow 22 develops in the orifice area of cavity 19 and in crossflow channel 33. In addition, in accordance with FIG. 2, the pressure fluctuation in the cavity leads to a greater pressure differential between gas flow 20 and cooling-air flow 21b, ultimately increasing leakage and resulting in a degraded efficiency of the fluid energy machine.